1. Field of the Invention
The present invention relates to a high strength steel having a borosilicate glass coating bonded thereto, which increases the ballistic efficiency of the steel, and which yields a highly wear-resistant material.
2. Description of Related Art
Ballistic steels have heretofore been developed for use as armor on military vehicles, among other things. The principal material properties which provide a steel with the ability to defeat various projectile threats are its high hardness, coupled with a high impact toughness or strength, and a uniformity of these properties throughout the material. As used herein, the term ballistic steel will generally refer to steels having a Brinell hardness of about 477 and above. In efforts to improve the ballistic performance of these steels, ceramics and aramids have been proposed for use in combination with the steel for ballistic reinforcement, but each of these types of materials has certain disadvantages for use in particular armor services, such as in underbody panels for relatively light vehicles.
Ceramic coating of steels is generally known in the art, primarily in services in which corrosion and/or abrasion resistance is required. However, as noted for example in U.S. Pat. No. 4,328,032, issued to Mancini et al., the process by which the ceramic coating is applied can cause the steel to lose its desired material properties.
Another problem with conventional ceramic coatings is that they often bond poorly to steel. Both the degradation of material properties and the poor bonding can give rise to unsatisfactory performance in resisting or defeating high blast forces and fragmentation-type threats. In fact, a poorly bonded ceramic coating would not likely hold up well in an underbody panel application against rocks and debris encountered in normal military transit. A cracked or spalled ceramic coating would reduce the ballistic properties of the panel to at or near the levels of the bare steel.
To the knowledge of the present inventor, because of problems such as poor bondability, the practical uses of ceramics in combination with ballistic steel for armor plate have been limited to applications in which preformed ceramic panels or plates are glued to the steel or are affixed thereto by mechanical means such as hook-and-loop (Velcro) fasteners.
The use of aramids as ballistic reinforcement material for steel plate is a very high cost solution, and for the most part, the increased cost cannot be justified in terms of the increased performance obtained.
Increasing the plate thickness of a ballistic steel will increase its ballistic properties, but with increased thickness comes the attendant increased weight. This is an undesirable solution in most instances, and is an unacceptable solution in certain instances. As an example, in the case of the military armored Hummer vehicle, supplied by AM General, it has been determined that increased underbody protection against fragmentation-type threats, which, in the case of pipe bombs and hand grenades, combine high blast forces and random-sized fragments travelling at high speed, is necessary. However, due to stringent weight requirements on that vehicle, it is not possible to simply provide a heavier-wall version of a ballistic steel armor employed as side armor on the vehicle.
Glass-coated steels have also been developed, outside the field of ballistic materials, for storage tanks and other storage structures, with the glass coating being provided principally as a corrosion resistant layer. One example of a glass-coated steel is used in the Harvestore.RTM. feed storage structure, which employs a Permaglas.RTM. borosilicate glass coating on both the inner and outer surfaces of the steel sheet. Harvestore.RTM. and Permaglas.RTM. are registered trademarks of the A. O. Smith Corporation, the manufacturer of the Harvestore.RTM. structure. The coating on the outer surface resists corrosion due to weather conditions, and the coating on the inner surface of the structure resists corrosive attack by materials stored therein. Such coatings have not heretofore been disclosed for use in ballistic material applications.
It is a principal object of the present invention to provide a glass-coated steel composite product having improved ballistic properties.
It is an additional principal object of the present invention to provide a glass coated ballistic steel composite product having improved capability to withstand and defeat fragmentation-type threats.
It is a further object of the present invention to provide an underbody panel for a vehicle having improved ballistic properties capable of providing protection against fragmentation-type threats to the occupants and/or cargo carried by the vehicle.
It is a further object of the present invention to provide a high strength, high toughness glass coated steel having an impact resistant and wear resistant glass coating thereon.